Solution for electrolytically removing chromium carbide coating and method for same

ABSTRACT

A solution and method for electrolytically removing chromium carbide coatings from the surface of substrates are provided. The solution includes 20-200 g/L alkali, the alkali being soluble alkali metal hydroxides; 20-150 g/L accelerant, the accelerant being a complexant and can combine with chromium ion; and 0.5-10 g/L auxiliary agent, the auxiliary agent being soluble polyphosphates. The method for removing chromium carbide coating on the substrate mainly includes electrolysis using the substrate having the coating as the anode and using the solution as the electrolyte.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is one of the five related co-pending U.S. patent applications listed below. All listed applications have the same assignee. The disclosure of each of the listed applications is incorporated by reference into all the other listed applications.

Attorney Docket No. Title Inventors US 33408 ELECTROLYTE FOR REMOVING TITANIUM- WEI HUANG CONTAING COATS AND REMOVING METHOD USING et al. SAME US 33410 SOLUTION FOR REMOVING TITANIUM-CONTAINING WEI HUANG COATS AND REMOVING METHOD USING SAME et al. US 33411 SOLUTION FOR REMOVING TITANIUM-CONTAINING WEI HUANG COATS AND REMOVING METHOD USING SAME et al. US 33412 SOLUTION FOR ELECTROLYTICALLY REMOVING WEI HUANG CHROMIUM CARBIDE COATING AND METHOD FOR et al. SAME US 33413 SOLUTION SYSTEM FOR ELECTROLYTICALLY WEI HUANG REMOVING TITANIUM CARBIDE COATING AND et al. METHOD FOR SAME

BACKGROUND

1. Technical Field

The present disclosure relates to a solution for electrolytically removing chromium carbide coating and a related method.

2. Description of Related Art

Hard ceramic coatings, such as chromium carbide, impart specific properties to workpieces such as machining tools, die core-pins, and high temperature devices. These hard coatings resist wear, abrasion, oxidation, and corrosion, and reduce susceptibility to chemical reactions with the workpieces to which they are applied. These coatings, however, can fail locally during use or manufacture.

Often, when such coatings fail, the entire die or tool component is discarded, even if the underlying substrate shows no damage, at considerable cost. For this reason, the ability to recycle the underlying substrate by removing a failed coating and replacing it with a new coating is economically preferable.

Therefore, there is room for improvement within the art.

DETAILED DESCRIPTION

The present disclosure relates to a solution and a related method for electrolytically removing chromium carbide coatings formed on the surfaces of substrates. The substrate may be metal or plastic. The metal may be ferric-based alloy (such as stainless steel), copper, or copper alloy.

The solution may be an aqueous solution containing alkali, accelerant, and auxiliary agent.

The alkali may be soluble alkali metal hydroxides, such as, sodium hydroxide, or potassium hydroxide, or a combination thereof. The concentration of the alkali selected may be about 20-200 g/L, and in this exemplary embodiment it is about 50-100 g/L. The alkali provides an alkali condition for the chromium contained in the coats to change to chromium ions during electrolysis process.

The accelerant may be a complexant capable of complexing with chromium ions, such as sodium potassium tartrate, sodium gluconate, sodium citrate, or ethylenediaminetetraacetic acid (EDTA), or a combination thereof, and preferably a combination of sodium gluconate and sodium citrate or a combination of sodium gluconate and EDTA. The concentration of the accelerant selected may be about 20-150 g/L and in this exemplary embodiment is about 40-100 g/L. The accelerant can combine with the chromium ions dissolved in the solution to form coordination compounds and facilitate a continuing dissolution of the chromium ions of the chromium carbide coating.

The auxiliary agent may be soluble polyphosphate, such as sodium tripolyphosphate (Na₅P₃O₁₀), or sodium pentapolyphosphate (Na₇P₅O₁₆), or a combination thereof, and preferably sodium pentapolyphosphate. The concentration of the auxiliary agent selected may be about 0.5-10 g/L, and in this exemplary embodiment is about 2-8 g/L. Inclusion of the auxiliary agent in the solution can facilitate rinsing the solution from the substrate after electrolyzation is completed, preventing damage to the substrate caused by any remaining solution.

The solution may be prepared by dissolving the alkali, accelerant, and auxiliary agent in water.

The method for removing the chromium carbide coating formed on the substrate may include steps of providing the solution, and removing the chromium coating by electrolysis using the substrate having the chromium carbide coating as the anode, and the solution as the electrolyte. The temperature of the solution during electrolysis is maintained between about 50° C. and about 95° C. Stainless steel or carbon material may be used as the cathode. The anodic current density is about 1-10 A/dm², and in this exemplary embodiment is about 4-7A/dm². After electrolysis, the substrate is rinsed with water and then dried. The coating can be effectively removed from the substrate and the underlying base is free from damage by the present method.

EXAMPLES

Experimental examples of the present disclosure following.

Example 1 1. Preparation of the Solution

70g sodium hydroxide was added into 500 ml deionized water at a low speed. Then, 50 g sodium citrate, 30 g sodium gluconate, and 2 g sodium pentapolyphosphate were added into the water solution and completely dissolved. The water solution was supplemented with deionized water to 1000 ml. The solution was formed.

2. Removal of Chromium Carbide Coatings

Samples of stainless steel substrate having a chromium carbide coating were provided. The coatings had a thickness of about 2 μm. Complete electrolytic removal of the chromium coatings was accomplished using the substrate as the anode, and the solution as the electrolyte, using an anodic current density of about 5 A/dm². A piece of carbon was used as the cathode. The solution was maintained at a temperature between about 60° C. and 70° C. It took about 6 minutes for complete removal of the coating. Then, the samples were taken out of the solution and were dried after being rinsed with water.

Example 2 1. Preparation of the Solution

60 g sodium hydroxide was slowly added into 500 ml deionized water. Then, 30 g sodium citrate, 40 g sodium gluconate, and 6 g sodium pentapolyphosphate were added into the water solution and completely dissolved. The water solution was supplemented with deionized water to 1000 ml. The solution was formed.

2. Removal of Chromium Carbide Coatings

Samples of stainless steel substrate having a chromium carbide coating were provided. The coatings had a thickness of about 2 μm. Complete electrolytic removal of the chromium coating was accomplished using the substrate as the anode and the solution as the electrolyte, using an anodic current density of about 5 A/dm². A piece of carbon was used as the cathode. The solution was maintained at a temperature between about 60° C. and 70° C. It took about 6 minutes for complete removal of the coating. Then, the samples were taken out of the solution and were dried after being rinsed with water.

Example 3 1. Preparation of the Solution

50 g sodium hydroxide was slowly added into 500 ml deionized water. Then, 20 g EDTA, 40 g sodium gluconate, and 4 g sodium pentapolyphosphate were added into the water solution and completely dissolved. The water solution was supplemented with deionized water to 1000 ml. The solution was formed.

2. Removal of Chromium Carbide Coatings

Samples of stainless steel substrate having a chromium carbide coating were provided. The coatings had a thickness of about 3 μm. Complete electrolytic removal of the chromium coating was accomplished using the substrate as the anode, and the solution as the electrolyte, using an anodic current density of about 6 A/dm². A piece of carbon board was used as the cathode. The solution was maintained at a temperature between about 60° C. and 70° C. It took about 5 minutes for complete removal of the coating. Then, the samples were taken out of the solution and were dried after being rinsed with water.

Examples 4-6

In examples 4-6, the solutions were respectively prepared according to the examples 1-3. Unlike the examples 1-3, the stainless steel substrate samples were replaced with carbon steel substrate samples. Except the above difference, the remaining experiment conditions of examples 4-6 were respectively the same as examples 4-6.

Results of the Examples 1-6

The samples processed in the examples 1-6 were inspected by X-ray diffraction (X-RD). No chromium was detected on the samples. Accordingly, the coatings were effectively and completely removed from the underlying substrates. Furthermore, the processed samples were scanned using scanning electron microscopy. The scanning indicated no corrosion found on the underlying substrates.

It is believed that the present embodiment and its advantages will be understood from the foregoing description, and it will be apparent that various changes may be made thereto without departing from the spirit and scope of the disclosure or sacrificing all of its advantages, the examples hereinbefore described merely being preferred or exemplary embodiment of the disclosure. 

1. An aqueous solution for electrolytically removing chromium carbide coatings from substrates, comprising: 20-200 g/L alkali, the alkali being soluble alkali metal hydroxide; 20-150 g/L accelerant, the accelerant being a complexant capable of combining with chromium ions; and 0.5-10 g/L auxiliary agent, the auxiliary agent being soluble polyphosphate.
 2. The aqueous solution as claimed in claim 1, wherein the alkali metal hydroxide is sodium hydroxide or potassium hydroxide, or a combination of the hydroxide and potassium hydroxide.
 3. The aqueous solution as claimed in claim 1, wherein the concentration of the alkali is about 50-100 g/L.
 4. The aqueous solution as claimed in claim 1, wherein the complexant comprises one or more of the group consisting of sodium potassium tartrate, sodium gluconate, sodium citrate, and ethylenediaminetetraacetic acid.
 5. The aqueous solution as claimed in claim 4, wherein the complexant is a combination of sodium gluconate and sodium citrate or a combination of sodium gluconate and ethylenediaminetetraacetic acid.
 6. The aqueous solution as claimed in claim 1, wherein the concentration of the accelerant is about 40-100 g/L.
 7. The aqueous solution as claimed in claim 1, wherein the polyphosphate is sodium tripolyphosphate or sodium pentapolyphosphate, or a combination of the tripolyphosphate and sodium pentapolyphosphate.
 8. The aqueous solution as claimed in claim 1, wherein the concentration of auxiliary agent is about 2-8 g/L.
 9. A method for removing a chromium carbide coating from a substrate, comprising: providing an aqueous solution containing 20-200 g/L alkali, the alkali being soluble alkali metal hydroxide, 20-150 g/L accelerant, the accelerant being complexant capable of combining with chromium ion, and 0.5-10 g/L auxiliary agent, the auxiliary agent being soluble polyphosphate; and removing the chromium coating by electrolysis using the substrate as the anode, and the aqueous solution as the electrolyte.
 10. The method as claimed in claim 9, wherein the alkali metal hydroxide is sodium hydroxide or potassium hydroxide, or a combination of the hydroxide and potassium hydroxide.
 11. The method as claimed in claim 9, wherein the concentration of the alkali is about 50-100 g/L.
 12. The method as claimed in claim 9, wherein the complexant comprises one or more of the group consisting of sodium potassium tartrate, sodium gluconate, sodium citrate, and ethylenediamine tetraacetic acid.
 13. The method as claimed in claim 9, wherein the concentration of the accelerant is about 40-100 g/L.
 14. The method as claimed in claim 9, wherein the polyphosphate is sodium tripolyphosphate or sodium pentapolyphosphate, or a combination of the tripolyphosphate and sodium pentapolyphosphate.
 15. The method as claimed in claim 9, wherein the concentration of auxiliary agent is about 2-8 g/L.
 16. The method as claimed in claim 9, wherein the electrolysis is carried out under an anodic current density of about 1-10 A/dm²
 17. The method as claimed in claim 16, wherein the electrolysis is carried out under an anodic current density of about 4-6 A/dm².
 18. The method as claimed in claim 9, wherein the solution is maintained at a temperature between about 50° C. and about 95° C. during electrolysis.
 19. The method as claimed in claim 18, wherein the solution is maintained at a temperature between about 60° C. and about 70° C. during electrolysis.
 20. The method as claimed in claim 9, wherein the substrate is selected from the group consisting of ferric-based alloy, copper, copper alloy, and plastic. 